Maya, the mother of Buddha died a week after Buddha was born. She was reborn in the Trayastrimsa Heaven as a god named Santusita. To honour his mother, Buddha ascended to the Trayastrimsa Heaven and preached from the Abhidhamma texts to Santusita for three months. 

Wan Kao Pansa marks the ascent by Buddha and the start of the three month period of Buddhist Lent when the monks retreat to their monasteries. During this time, monks dedicate themselves to meditation and study. During Buddhist Lent, marriages are forbidden and many people give up meat and alcohol. Buddhist lent often coincides with the rainy season in Lao. 

Boun Ok Phansa marks Buddha’s return to earth and signifies the end of Buddhist Lent when after three months of retreat, the monks return to their daily social activities. 

At dawn of Boun Ok Phansa, followers gather at temples across Lao to give donations and offerings. 

In the evening, beautiful candlelit processions are held at the temples and hundreds of colourful floats of flowers, incense and candles float down the Mekong River. To prepare for the celebration, families make a small round container to put candles, flowers, incense or food and money. 

At the bank of the Mekong, they then light the candles, say prayers and send the boat of light floating away down the river.  

This tradition is observed to pay respect to the river spirits, especially the Mekong River which means Mother of All Things. People also believe that this is a way to send away all negativity such as sickness, bad luck, shortcoming, and failure. 

The end of Buddhist Lent is also celebrated with fabulous boat races along the Mekong River in Vientiane.